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We provide a comprehensive overview of recent progress in this rapidly growing field by summarizing catalytic annulation reactions of ortho-alkynyl aryl ketones which involve carbo- and oxo-cyclization patterns with consideration of their mechanisms and applications.

A new gold(i) self-relay catalysis reaction enabling the annulative oxygenation of propargylic alcohols with various O-nucleophiles, such as carboxylic acids, alcohols and TBHP, is reported, producing a series of functionalized benzofurans.

A novel gold(i)/Brønsted acid relay catalysis enabling azofuran activation to induce annulative rearrangement from 3-yne-1,2-diols is reported, producing a series of furan-2-yl-substituted pyrrol-2-ones with good yields.

Two catalytic benzannulation/1,4-addition cascades of available enynones with indoles or tetronic acid-derived enamino lactones as C-nucleophiles are reported, producing 53 examples of heterocycle-incorporating diarylmethanes with moderate to excellent yields. The combination of AgOTf and Sc(OTf)3 permits bimetallic synergistic catalysis of the reaction of enynones with indoles to access 35 triarylmethanes in generally good yields with ortho-naphthoquinone methides, generated in situ, as the key intermediates. Exchanging indoles for tetronic acid-derived enamino lactones resulted in 18 diarylmethanes by the Ag-catalyzed benzannulation/1,4-addition cascade. Both reactions are advantageous for their high atom utilization and mild reaction conditions, providing intriguing complementary approaches for the direct syntheses of new heterocycle-containing diarylmethanes.

A new gold(i) self-relay catalysis consisting of a 3,3-rearrangement, Nazarov cyclization and Michael addition cascade of 1,3-enyne acetates with aurones and their derived azadienes is reported, producing functionalized cyclopentenones.

A new electrochemical selective annulative amino-ketalization and amino-oxygenation of 1,6-enynes with disulfonimides and alcohols is reported, producing a series of functionalized benzofurans under catalyst- and oxidant-free conditions. The annulative aminoketalization proceeds with simple short-chain alcohols such as methanol, ethanol and

A new asymmetric catalytic conjugate reduction of yne-allenones to synthesize enantioenriched cyclobuta[a]naphthalen-4(2H)-ones has been established that uses copper-bisphosphine complexes as catalysts and gives excellent regio- and enantioselectivities (≥99% ee) in most cases. This protocol tolerates a broad scope of substrates, exhibits high compatibility with various substituents, and gives excellent stereoselectivity, providing a catalytic and efficient entry to fabrication of synthetically important chiral 6-6-4 tricarbocyclic scaffolds.

A new Lewis acid-catalyzed [2 + 2] cycloaddition/retroelectrocyclization (CA-RE)/1,6-addition relay of aurone-derived 1-azadienes and 1-alkynylnaphthalen-2-ols has been reported, leading to the regio- and diastereoselective synthesis of 1,2-dihydrobenzofuro[3,2-b]pyridine with a chiral carbon center and an axial chirality in good yields. This protocol enables the C-C double-bond scission/recombination to rapidly construct aza-heterocyclic architectures and features 100% atom utilization, a wide substrate scope, good compatibility with substituents, and excellent diastereoselectivity.

Tunable electrocatalytic annulation reactions of o-arylalkynylanilines have been established, leading to green and divergent syntheses of skeletally diverse indoles by adjusting the electrolytes and the solvents. The presence of ammonium halides as the electrolytes enabled the halogenation of o-arylalkynylanilines to give C3-halogenated indoles whereas naphtho[1',2':4,5]furo[3,2-b]indoles could be obtained by changing the electrolyte from ammonium halides to KI. Interestingly, by combining acetone as the solvent and both NH4I and NH4Cl as the electrolytes, the reaction worked through an intramolecular annulation and [5 + 1] cyclization cascade to form naphtho[1',2':5,6][1,3]oxazino[3,4-a]indoles.

A new photocatalytic three-component annulation of 2-alkynylaryldiazonium tetrafluoroborates with γ-hydroxyl terminal alkynes and sodium metabisulfite is reported using fac-Ir(ppy)3 as the photocatalyst for the first time and used to produce a series of (Z)-thiochromene 1,1-dioxides bearing an exocyclic double bond with moderate to good yields in a highly stereoselective manner. A wide variety of easily available substrates with substituent diversity could successfully participate in this photocatalysis with good functional group tolerance.

A new and general photocatalytic Kharasch-type addition/1,5-(SN'')-substitution cascade of 1,7-diynes with alkyl halides such as BrCCl3 and CBr4 was reported for the first time, and used to produce 65 hitherto unreported β-gem-dihalovinyl ketones/aldehydes with moderate to excellent yields in a highly regioselective manner. This reaction tolerates a wide scope of substrates, which offers a green and efficient entry to fabricate synthetically important β-gem-dihalovinyl carbonyl scaffolds. Notably, the late-stage application of these resulting β-gem-dihalovinyl carbonyls shows high and unique reactivity profiles and demonstrates the versatility of their derivatization.

New tunable catalytic [2+2] cycloaddition/silane-mediated conjugate transfer reductions of yne-allenones have been developed, by which substituent-diverse cyclobutarenes with generally good yields were selectively synthesized by adjusting Fe-H and Cu-H catalytic systems. Use of the Fe-H system triggers 1,6-conjugate reduction to dihydrocyclobuta[a]naphthalen-4-ols whereas the Cu-H complex enables 1,4-conjugate reduction to cyclobuta[a]naphthalen-4(2H)-ones.

A new copper/silver-co-mediated three-component bicyclization of benzene-linked 1,6-enynes with ICF2CO2Et with TMSN3 was reported, and used to produce a wide range of hitherto unreported difluorinated tetrahydroindeno[1,2-c]azepine-3,6-diones with moderate to good yields. The mechanistic pathway consists of radical-induced 1,6-addition–cyclization, oxidative addition, reductive elimination, nitrene insertion and N–O cleavage, resulting in continuous multiple bond-forming events including C–C and C–N bonds to build up a 6/5/7 tricyclic framework.

A new chelation-controlled hydrofuranization of unactivated olefins with α-alkynyl arylols is reported for the first time, and used to produce a wide range of C3-alkylated benzofurans with generally good yields under mild conditions. A bidentate directing group is used to suppress β-hydride elimination and in turn facilitate a protodepalladation event. In addition to 100% atom utilization, good functional group tolerance and mild conditions, the present catalysis did not demand any additional ligand, additives and bases/acids, making the transformation simple and facile and it thus opens new avenues for catalytic difunctionalization of alkynes and olefins.

Photoinduced arene–alkyne [3 + 2] cycloaddition cascades of 1-alkynylnaphthalen-2-ols without a photosensitizer were developed for the first time, enabling tunable synthesis of skeletally diverse bridged hexacyclic architectures with good yields and complete stereoselectivities through solvent-dependent divergent dearomatized cyclodimerizations. The photocatalysis in N,N-dimethylformamide (DMF) delivered functionalized bicyclo[3.2.1]octane-containing bridged oxa-heterocycles, whereas tetrahydrofuran (THF) oriented high stereoselectivity to offer bridged carbocycles. The reaction pathway generates two classes of complex three-dimensional structures that evolve from the same planar internal alkynes.

A new copper-catalyzed radical-triggered fluoromethylation-spirotricyclization of enediyne- and enyne-nitrile-containing para-quinone methides (p-QMs) was reported for the first time, and used to produce a series of hitherto unreported cyclohexadienone-based pentacyclic spiroindenes with moderate to good yields and complete regioselectivity. The reaction proceeds through a complex difluoromethyl or trifluoromethyl radical-induced 1,6-addition/5-exo-dig, 6-exo-dig, 6-endo-trig tricyclization/single electron transfer (SET) process, resulting in the direct formation of up to three new rings and four chemical bonds in one step. The present Cu-catalyzed strategy accommodates a good substrate scope and is distinguished by its high bond-forming efficiency, annulation efficiency, and high regioselectivity.

The combination of Pd(TFA)2 and an N,N′-disulfonyl bisimidazoline ligand shows high catalytic activity and excellent asymmetric induction in the addition of arylboronic acids to cyclic N-sulfonyl k...

Two classes of new catalytic spiroannulation-fluormethylfunctionaliztions of para-quinone methide (p-QM)-containing 1,5-enynes have been established under redox-neutral conditions. Palladium-catalyzed spiroannulation-iododifluoromethylation with ethyl difluoroiodoacetate oriented completely stereoselective access to (Z)-spiroindenes and the latter included copper-catalyzed three-component spiroannulation-cyanotrifluoromethylation starting from Togni's reagent and trimethylsilanecarbonitrile (TMSCN). Both reaction pathways involve fluoroalkyl radical-triggered 1,6-addition/5-exo-dig annulation/metal radical cross-coupling/reductive elimination sequence, providing practical and stereoselective protocols for rapidly constructing cyclohexadienone-containing spiroindenes with generally good yields.